A STUDY OF THE NERVOUS SYSTEM 271 



and tenth) are both afferent and efferent (or mixed nerves) 

 and in this respect resemble the spinal nerves. 



Frog Physiology. We are probably indebted to the com- 

 mon frog more than to any other animal for our knowledge 

 of general physiology. Countless experiments have been 

 performed upon its skin, its muscles, its sense organs, and 

 its central nervous system. Some of these experiments 

 which throw light upon the functions of the various parts 

 of the brain and spinal cord will now be described. 1 



Functions of the Spinal Cord. When we separate the whole 

 brain from the spinal cord by making a cut just behind the 

 medulla, the " frog will still continue to live, but with a very 

 peculiarly modified activity. It ceases to breathe or swal- 

 low; it lies flat on its belly> and does not, like a normal 

 frog, sit up on its fore paws, though its hind legs are kept, 

 as usual, folded against its body, and immediately resume 

 this position if drawn out. If thrown on its back, it lies 

 there quietly, without turning over like a normal frog. 

 Locomotion and voice seem entirely abolished. If we 

 suspend it by the nose, and irritate different portions of 

 the skin by acid, it performs a set of remarkable ( defensive' 

 movements calculated to wipe away the irritant. Thus, if 

 the breast be touched, both fore paws will rub it vigorously ; 

 if we touch the outer side of the elbow, the hind foot of the 

 same side will rise directly to the spot and wipe it." 



Functions of the Hindbrain and Midbrain. "If, in a 

 second animal, the cut be made just behind the optic lobes 

 so that the cerebellum and medulla oblongata remain at- 

 tached to the cord, then swallowing, breathing, crawling, 

 and a rather enfeebled jumping and swimming are added to 

 the movements previously observed. . . / The animal, 

 thrown on his back, immediately turns over to his belly." 

 If the cut be made on another frog just in front of the optic 

 lobes, " the locomotion both on land and water become quite 



1 In this account we shall quote from a most interesting book by 

 Professor William James (' Psychology," Vol. I. Henry Holt & Co.> 



